Apparatus for checking the contamination condition of electric insulators

ABSTRACT

The apparatus comprises a probe-insulator (3) with an internal cavity, a first system (8/1) that circulates a cold fluid within the cavity (4) of the probe-insulator in order to cool the latter to such a temperature that the external humidity condenses on the external surface, a second system (8/2) for measuring the surface conductivity on the probe-insulator, a third system for activating a washing plant of all insulators installed in the same area when the measured value of said surface conductivity reaches a pre-set critical value; the refrigerating device that produces said cold fluid preferably includes a group of Peltier modules.

The present invention relates to an apparatus for checking thecontamination condition of electric insulators installed in the open ina given area, for instance the insulators of an electric station orsub-station.

In the following description, with insulators we intend those units madeof porcelain, glass or other suitable insulating materials that affordthe electrical insulation between two parts at different voltage of anopen air electric plant.

A thorough checking of the contamination conditions of the externalsurfaces of such insulators allows the piloting of cleaning actions onthe same insulators. It is noted that a drop in the insulatingproperties of an insulator also occurs when the contaminator deposit onits surface exceeds the critical threshold that depends on the shape andsize of the insulator and on the voltage applied. This has led to thedemand for an indicator of the quantity of contaminator deposit to befound on one insulator representative of a group of insulators installedwithin the same area and able to signal the moment in which said layerof deposit reaches the critical threshold and thus to activate thecleaning system action or, in absence of the latter, the start up of acleaning action of the insulator group with voltage disconnected. In thedescription that follows we shall call "the probe-insulator" aninsulator that is representative of the group of insulators in the samearea, group that will normally be made up of insulators of differenttype and shape.

It appears that there are no such quantity indicators installed inItaly, but elsewhere there are apparatus that function as quantityindicators of the contaminator deposit. A first system is noted,comprising a probe-insulator exposed at a given height from the groundin the plant area and that is periodically lowered into an underlyingtank so as to be washed in the water with the help of auxiliary meanssuch as ultrasonic waves and the rotation around its axis of theinsulator itself. All the contaminator materials deposited on theprobe-insulator's surface gets washed into the water. At the end of eachperiodic wash the volume conductivity of the solution is measured, andthis, naturally, tends to increase after each wash. In one instancecomes the time when the measured value for conductivity is equal to thepre-set critical threshold. A second system is also noted that comprisesa probe-insulator that, after being exposed, again at a certain heightwithin the plant area, is periodically lowered and closed into a chamberin which steam, produced by a steam generator, humidifies thecontaminator layer on the surface of the probe-insulator. Then theconductivity of this layer is measured and compared with the pre-setcritical threshold.

A common disadvantage of both these systems consists in the mechanicalcomplexity required for the automatic performance of the operativestages. For example, both the washing chambers and the humidifyingchambers need devices for their opening and closing; especially thefirst must be kept closed and must open only for the time necessary toallow the entrance of the probe-insulator, and the systems must comprisemechanisms and control means for the movements of the probe-insulatorrelatively to the chambers. Another disadvantage of the first systemrelates to the fact that its use is limited to those cases in which thecontaminator is easily soluble in water, as are generally marinepollutants. Another disadvantage pertaining to the second system is theneed to adjust the steam generator in relation with the environmentalconditions and the fact that this adjustment is made more complex and ofuncertain result because the system works in the open; moreover,experience has proved the difficulty of completely humidifying thecontaminator layer and, at the same time, avoiding that this layer bepartly or totally washed away.

The invented apparatus obviates the aforementioned disadvantages and, asclaimed, comprises: a probe-insulator featuring an internal cavity; afirst system for the circulation within this internal cavity of arefrigerating fluid that will cool the probe-insulator to such atemperature that the outside humidity will condensate onto its externalsurface; a second system for measuring the surface conductivity of theprobe-insulator cooled by said previous system; a third system formeasuring the temperature and relative outside environment humidity, foractivating said first and second systems proceeding to the survey,according to a pre-set sequence, of the probe-insulator's surfaceconductivity that has been cooled by the first system in order to reacha rating value for the conductivity, arresting the functions of saidfirst system and said second system and compare the said rating valueagainst a pre-set critical conductivity value producing an alarm signalas soon as said critical value is reached in order to activate acleaning system for the insulators installed in the area or, in absenceof the latter, the start up of a cleaning action of the same insulatorswith voltage disconnected.

The main advantages of the invented apparatus lie in the fact that onecauses the humidifying of the contaminator deposit on theprobe-insulator in a gradual and very close to natural process such asdew or fog that are the more frequent cause for insulator discharge; theduration of humidifying is accurately controllable and this avoids risksof washing out the surface of the probe-insulator during and afterhumidifying; the apparatus is highly reliable and simple in both itsbuild-up and functioning.

The above advantages and still others will become apparent in thefollowing description of one of the ways of realizing the invention withreference to the attached drawings that show specific realizations inwhich

FIG. 1 is an overall diagrammatic view of a first realization,

FIG. 2 is a diagram of a second realization, and,

FIG: 3 is a general diagram.

FIG. 1 shows: a) a support column 1 that carries an insulating shoe 2 atits top located at about 7 m. from the ground, within the yard of anelectric substation; upon said shoe 2 a probe-insulator 3 is installedas defined above, with a pattern that is representative of the otherinsulators installed in the same area and that bears an internal cavity4 with a profile that evidently follows the pattern of the outsideprofile (this probe-insulator 3 is 30 cms. high and has leak line ofabout 50 cms.); b) a tubular body of insulating material 5 with.projections 6, corresponding to the ribs 7 of the probe-insulator, ispositioned within the latter through shoe 2; c) a first system 8/1 forthe cooling comprising a conventional refrigerating device 9 (invertedCarnot cycle) the evaporator of which is associated with a heatexchanger within a unit 10; said first cooling system 8/1 gives arefrigerating fluid contained in the refrigerating device 9 atemperature of about 15° C. less than the temperature of the airsurrounding said probe-insulator; by means of a pump 11, said systemcauses said refrigerated fluid to circulate in said internal cavity 4through the inlet pipe 12 that enters the bottom side of the tubularbody 5, follows the route shown by arrow F1 and ends up in the returnpipe 13, according to arrow F2; d) a second system 8/2, shown in detailin the drawing FIG. 3, to measure the surface conductivity of theprobe-insulator 3; in the figure only a voltage generator 14 for atleast real 10 kV and an ammeter 15 fitted in an A-B circuit closedcircuit between the top and the base of the probe-insulator 3 are shown.

FIG. 2 is the diagram of the refrigerating device of an apparatus thatis perfectly similar to the one shown in FIG. 1, but in which therefrigerating device is realized with Peltier modules. As is known,according to the Peltier effect, at the contact surface between twoconductors of different composition, passed through by continuouselectricity heat is generated or absorbed, according to the direction ofthe current. Industry currently produces Peltier modules for diversetechnical appliances and the device shown comprises a refrigeratingsystem 16 that uses 20 Peltier modules 17, each made up by about 70bismuth-tellurium thermo-couples, dimensions of the latter 29×22×5 mms.,connected in parallel and fed by a continuous 12 V current from a source18. Said pump 11 causes the refrigerated fluid to circulate within thecavity 4 of the probe-insulator 3 (not shown), through said pipes 12 and13 and within the heat exchanger 19. One wall of said heat exchanger 19is adjacent to the cold walls 20 of the 20 Peltier modules so that thefluid can be cooled to a temperature about 15° C. lower than that ofenvironment temperature. The heat drawn from the fluid plus the thermalequivalent of the feed energy for the Peltier modules is dissipated inan exchanger 20.

FIG. 3 is a general diagram of an apparatus in which the refrigeratingdevice is realized with 20 Peltier modules 17, as illustrated in FIG. 2.It is clear however, that with minor changes, this drawing also appliesto an apparatus in which the refrigerating device is realized in aconventional manner, as shown in FIG. 1. The drawing is easilyunderstandable so only the main parts are listed and the function ofonly some of these are explained. On an insulator 20, supported by acolumn C, a probe-insulator 3 is installed, identical to the one shownin FIG. 1 and associated to said unit of 20 Peltier modules 17, aspreviously described. The rest of the apparatus comprises: a transformer21 that keeps the probe-insulator 3 at a voltage of 10 kV; fuses 22protecting the feeding circuit of the transformer 21 and a signal 23placed in a visible position to signal the possible burning out of saidfuses; a sectioning and distribution panel 24 that is used to sectionthe incoming electric lines to 220V/40A and 220V/6A that feed the staticno-break unit 25 that supplies reserve power in case of networkinterruption and an electronic box 26 to control the apparatus; a box 27to convert the measurement of the surface voltage into a digital signal;a thermo-hygrometer 28 to supply the values of relative outsideenvironment temperature and humidity; an anemometer 29 to supply windspeed values; a module 30 to perform the comparison between the valuemeasured and the memorised critical threshold and possibly start off analarm signal; a unit 31 to provide continuous current power to thePeltier modules 17.

The embodiment shown in FIG. 2 adds other advantages to the onesmentioned above: the apparatus is very compact and the refrigeratingsystem is totally static; faults in the refrigerating device are farless frequent and more easily repaired. Finally, the dia-thermal fluidused for refrigeration in Peltier modules is not a pollutant, differingas such from the conventional refrigerating fluids currently beingaccused for ecological reasons.

I claim:
 1. An apparatus for checking the contamination conditions ofelectric insulators by measuring the quantity of contaminator materialdeposited on the external surface of a probe-insulator (3), whichapparatus comprises: a probe-insulator (3) in a fixed position featuringan internal cavity (4); a first system (8/1) that circulates within thecavity (4) a cold fluid for cooling the probe-insulator (3) to atemperature such that the outside humidity condenses on the externalsurface of the probe-insulator; a second system (8/2) to measure thesurface conductivity of the probe-insulator cooled by said first system(8/1); a third system that generates an alarm signal at the moment inwhich the surface conductivity measured on said cooled probe-insulator(3) reaches a pre-set critical conductivity value and hence activates anautomatic washing plant for the insulators installed in that same areaor commands a cleaning operation with insulators disconnected.
 2. Anapparatus according to claim 1 which comprises a system for measuringthe outside environment relative temperature and humidity, to activatesaid first (8/1) and second (8/2) systems according to a pre-setsequence for the measurement of surface conductivity values on saidcooled probe-insulator (3) until a measured value for said conductivityis obtained, to stop the action of said first (8/1) and second (8/2)systems and hence compare said measured value with the pre-set criticalconductivity value and produce an alarm signal at the moment themeasured value reaches the critical value so as to activate a washingplant for the insulators installed in that same area or command awashing operation with the same insulators disconnected.
 3. An apparatusaccording to claim 1 characterized in that said first system (8/1)includes a conventional inverted Carnot cycle (9, 10) refrigeratingdevice.
 4. An apparatus according to claim 1 characterized in that saidfirst system (8/1) includes a refrigerating device (16) that employs anumber of Peltier modules (17).